The present invention relates to a progressive ophthalmic lens and in particular an ophthalmic progressive lens exhibiting improved optical performance in the distance viewing region. It is a feature of the present invention to provide spectacles designed specifically for distance and intermediate vision and providing improved flexibility for the wearer, with an improved angular range of visual fields and greater tolerance to fitting variability.
Numerous progressive lenses are known in the prior art. A progressive lens in general exhibits a distance and intermediate viewing zone in which the intermediate zone joins the intermediate and distance zones in a cosmetically acceptable way, in the sense that no discontinuities in the lens should be visible to people observing the lens of the wearer. The intermediate zone should be optically acceptable in the sense that there should be a line or corridor called the eye path along which the line of vision moves while going between the distance and intermediate zones, and along which the optical power of the lens increases more or less uniformly. It is normal to select an eye path with a slant to accommodate the natural convergence of the eyes along the path.
However, in order to provide at least acceptable distance and intermediate viewing zones compromises may need to be made to any or all zones.
Moreover, in the prior art, in order to provide a range of distance and intermediate zone optical powers which permit optimum fitting of the lens to most patients, a large family of progressive lens blanks with different distance and intermediate zone powers have been necessary. It would be a significant advance in the art if an ophthalmic lens could be designed which requires a smaller family of individual lens types to satisfy the distance and intermediate viewing needs of a wide range of patients. This would be more nearly similar to the number of blanks in a single vision reading lens series.
In the prior art, the large power change between the distance and intermediate viewing zones results in large aberrations which greatly restrict the permissible fitting positions for the lens.
It would be a significant advance in the art if an ophthalmic lens could be designed with reduced sensitivity to horizontal fitting errors (such as errors in pupillary distance measurement of the wearer) and vertical fitting height errors ascribed to frame and face conformation measurement errors. This would make such lenses more similar in ease of fitting to single vision reading lenses.